Somebody disagreeing with you isn't unassailable truth. I could introduce myself as Oli, and as many times as you tell me my name is Brian, that's not going to affect my knowledge of what my name is. Same here. Despite them being told, you will struggle to prove the plaintiff here does not truly believe they hold the IP for this game.

Intent is important because it's the motive to fraudulently file. It's the closest you'll get to proving what somebody knew, unless they confess.